This invention relates to packaging machines of the form-fill-seal type using a web of flexible thermoplastic film in the form of a roll and adapted to unwind the film from the roll to form it into a cylindrical tubular shape and thermally seal it after objects to be packaged are deposited inside. This invention relates more particularly to devices adapted to be used in connection with a packaging machine of this type for displaying the amount of the web currently remaining in the roll or outputting an alarm signal for indicating that the roll which is currently being used will be used up within a specified short period of time, as well as packaging machines incorporating such devices.
Packaging machines, for example, of a vertical pillow type as disclosed in U.S. Pat. Nos. 5,279,098 issued Jan. 18, 1994 and 5,347,795 issued Sep. 20, 1994 (which are herein incorporated by reference) carry a rolled web of an elongated film and are adapted to form the film into a cylindrical shape and to seal it transversely as objects to be packaged are dropped inside. When such a packaging machine is being operated, it is important to be able to predict at each moment how much film still remains in the roll thereon or how many packaged products can still be formed before the web in the roll currently installed thereon will be used up. Because the user will have to supply a new roll or stop the operation of the packaging machine for this purpose, it is also important for the user to be warned when the end approaches of the roll currently being used.
Japanese Patent Publication Tokko 5-305 disclosed a device for calculating the time required for using up a currently installed web roll from its current radius and the time required for it to make one complete rotation as the web is being pulled out thereof. Such a device, however, would require not only a non-contact sensor for detecting the radius of the web roll but also adjustments of the sensor such that it will function properly all the time. Moreover, the user with such a device cannot predict how much web still remains in the roll or how many products can still be made from the web of film remaining in the roll.